Conventional polymeric substrates or polishing pads used for polishing, planarizing and other operations for which the present article is useful may be subjected to a variety of operating conditions which influence the selection of the substrate material. For example, variations in the nature of the workpiece being polished, polishing speed and pressure, elevated temperatures generated during the polishing operation, and the nature of any polishing slurry used in the operation may influence the choice of substrates.
Conventional polymeric polishing pads often vary in quality due to imprecise control of polymerization and blending processes and cutting and shaping of the final pad product. Therefore, the polishing characteristics imparted to a workpiece being polished, such as surface quality, stock removal rate and planarization rate, typically vary greatly between pad batches.
Conventional polishing pads are generally formed from multilayer laminations or stratified substrates having non-uniform physical properties throughout the thickness of the pad. An example of a typical stratified pad widely used for polishing semiconductor devices is the Politex Supreme pad, which is commercially available from Rodel Incorporated, of Newark, Del. A typical Politex Supreme pad is composed of several layers, including a firm but resilient, 1 mm to 2 mm thick, porous bottom layer comprised of a polyester felt and polyurethane binder. A spongy and resilient microporous urethane layer of about 0.05 mm to 0.3 mm thickness is laminated onto the bottom layer. The top layer is comprised of vertical urethane structures having vertical, tapered pores, the taper of the pores narrowing toward the top of the pad. The top layer is very soft, porous and elastic. In a typical polishing operation, the top layer of such a stratified pad wears rapidly. As the top layer wears and subsequent layers are exposed, the polishing properties of the pad vary, resulting in non-uniform polishing rates and producing inconsistent polishing characteristics on the surface of the workpiece.
Conventional polishing pads typically have textured surfaces. The "microtexture" of a pad is the intrinsic microscopic bulk texture of the pad after manufacture. Some of the factors which influence the static morphology or microscopic bulk texture of a conventional pad are the nature or texture of the work surface, such as waves, holes, creases, ridges, slits, depressions, protrusions and gaps, and the size, shape, and distribution, frequency or spacing of individual features or artifacts. In typical polishing pads, the microtexture of the pad is largely random and is the result of factors intrinsic to the manufacturing process. Because of the large number of variables in the manufacturing process, few attempts have been made to Control variables such as pore size, shape and distribution. Other characteristics which may affect the pad texture are hardness, resilience, thickness, permeability, and resistivity, to name a few.
"Minitexturized" pads have intermediately sized textured artifacts on the pad, which may be produced by use of lasers or the incorporation of air or gas within the pad material.
"Macrotextures", or larger size textured artifacts, may be imposed on the work surface of a pad by embossing, skiving, perforating and/or machining, for example. In conventional polishing pads, the spacing and/or size of individual macrotexture artifacts or features is generally greater than 5 mm. The spacing and size of these artifacts are typically very regular and repetitive.
Conventional polishing pads may include various solid particulates, such as cerium oxide, titanium oxide, aluminum oxide, barium carbonate, glass dust and fibers, diatomaceous earth, rouge, calcium carbonate, diamond, and carbon, for example. Typically, mechanical mixing and distribution of such particulates has been poorly controlled.
It would be desirable to have a substrate for polishing and other operations in which the particle distribution of additives may be optimized on a molecular scale. It is also desirable to have a polymeric substrate in which the surface of the substrate regenerates itself and does not vary appreciably as the surface is contacted with a workpiece. A polishing substrate which has a series of hardness variations on a micro scale and which can be texturized on a mini or macro scale to help remove dross (effluent, grindings, etc.) during polishing operations would also be advantageous.